Localised immune complexes and slipped upper femoral epiphysis.

Slipped upper femoral epiphysis remains a disease of unknown aetiology. Recent evidence has bolstered speculation that the immune system may play a role in the aetiology or pathogenesis of slipped epiphysis or of one of its complications, chondrolysis. This study reports the finding of immune complexes in the synovial fluid of all but one hip affected with slipped epiphysis in a consecutive series. In seven patients, immune complexes were detected by both the Raji cell assay and C1q-binding assay; in two, by the C1q-assay only; and in one, by the Raji cell assay only. No patients had immune complexes in the serum. Twenty-one patients with synovitis of the knee or hip caused by a variety of disorders served as the control group. Two of these patients had immune complexes in their synovial fluid. It appears that the immune complexes characterise the synovitis found with slipped upper femoral epiphysis as distinct from most other synovitides.